Prevent 6:1 trial: pI rotocol for a feasibility trial of a 6:1 intermittent diet for weight gain prevention in women at increased risk of breast cancer

Introduction Weight gain in adulthood is a common potentially modifiable breast cancer risk factor. Intermittent 5:2 diets (two low-calorie days/week) have proven efficacy for weight loss among people with overweight or obesity and can promote sustained awareness and mindfulness of diet choice and help appetite control.

This trial aims to test whether a less intensive 6:1 intermittent diet programme (one low-calorie day/week) is a feasible intervention to promote healthy eating and prevent weight gain in women at increased risk of breast cancer. Methods and analysis Single arm prospective feasibility trial in 30 healthy weight women aged 18 - 40 years, at moderate or high risk of breast cancer (≥17% lifetime risk and/or ≥3% 10 year risk at 40 years), body mass index 20 - 25 kg/m 2 .

Participants will be entered to a 16-week 6:1 diet programme involving 1 day consuming 1000 kcal and healthy eating for 6 days a week. Participants will also be advised to meet physical activity recommendations for health (≥150 min of moderate intensity physical activity/week and resistance exercise two times per week).